The present invention relates to a method of improving the water absorbent properties of cellulose-containing material.
Numerous methods have been proposed heretofore for increasing the water absorbency or hydrophilicity of cellulose-containing materials. More recently, these efforts have centered around graft-copolymerizing onto the cellulose-containing material monomers containing hydrophilic groups. Following the graft copolymerization step, the hydrophilic groups impart to the material various degrees of water retentive properties.
In the Journal of Applied Polymer Science, Vol. 17 (1973) at pages 3143-3156, Lepoutre et al describe a method for increasing the water absorbency of wood pulp by grafting thereon polyacrylonitrile and subsequently hydrolizing the material to a sodium polyacrylate-polyacrylamide copolymer. Williams et al. [Journal of Applied Polymer Science, Vol. 10, pages 1229-1245 (1966)] describe a method for modifying the wool-water relationships by grafting techniques. U.S. Pat. No. 3,423,163 to Magat et al describes a method for increasing the moisture absorption properties of cellulose materials by graft copolymerizing thereon N-methylolacrylamide.
U.S. Pat. No. 3,252,880 to Magat et al. discloses that a base polymer may be rendered more hydrophilic by grafting thereon suitable monomeric materials. U.S. Pat. No. 3,514,385 to Magat et al. discloses the grafting of various acrylic compounds to cellulosic base materials in order to increase the hydrophilicity of the resulting product. U.S. Pat. No. 3,201,336 to Magat et al. also discloses grafting acrylic monomers onto cellulosic based materials.
While all of these methods operate to impart some degree of increased hydrophilicity to the materials treated, there has not as yet been proposed a method for drastically increasing the water absorptive properties or hydrophilicity of cellulose-based materials to the extent required in some applications of the cellulose material. For example, a high degree of water absorption is required of disposable diapers comprising cellulose materials. The preparation of catamenial receptors, surgical swabs, etc., also requires the utilization of highly absorptive cellulose materials.